1. Field of the Invention
The present invention relates to the utilization of photocatalytic action to bleach and remove colored sediment on (stained or discolored) teeth, and more particularly to a method for bleaching discolored teeth comprising the steps of applying a bleaching agent comprising a specific composition having photocatalytic action on the surface of discolored teeth, and bleaching the teeth based on the photocatalytic action that is produced by irradiating this area with light; a novel bleaching agent comprising a solution/paste of 3% or less aqueous hydrogen peroxide and titanium dioxide producing photocatalytic action when irradiated with light, which is useful for such bleaching; a method for producing such a bleaching agent; and a bleaching system comprising a combination of the aforementioned bleaching agent and the like.
2. Description of the Related Art
There has been increasing demand in recent years for improvements in the contour, alignment, and integrity of teeth in dental therapy, which may be referred to as cosmetic improvements. Recently there have been more cases of patients seeking dental therapy based on a desire for whiter teeth, which is increasingly regarded by young women as an important element of beauty. The causes of dental discoloration and pigmentation or staining are generally classified into so-called extrinsic factors, such as the sedimentation of colored substances (tobacco, tea, etc.), pigment generating bacteria, the discoloration of repair materials (primarily composite resins), and metal salts (primarily amalgams, silver nitrate, and ammonia silver), and intrinsic factors, such as aging, chemicals or drugs (such as fluorine and tetracyclines), dysmetabolism and hereditary diseases, and dental injuries. The latter intrinsically discolored teeth are indicated for bleaching methods to which dental health system treatment is applied.
Several methods have been proposed in the past as methods for the cosmetic improvement of discolored teeth, among which bleaching may be considered a highly effective method for the preservation of dentine, despite drawbacks such as occasional recurrence, when methods suited to individual cases are selected and properly carried out.
Bleaching is essentially a method for decolorizing colored substances by means of a chemical reaction. In the past, there have been various reports of bleaching agents comprising a variety of chemical agents based on vital bleaches and non-vital bleaches, as well as bleaching methods involving the use of such agents.
The following are some typical examples.
1) Bleaching which features the use of 30% H.sub.2 O.sub.2 as the chemical agent, and the combined use of light and heat on the aqueous hydrogen peroxide.
This is a method in which strips of gauze soaked in 30% H.sub.2 O.sub.2 are placed on the front surface of the teeth and are irradiated for 30 minutes from the left and right by two 500 W photographic lamps. In this method, the lamps are brought as close as possible, and the H.sub.2 O.sub.2 must be replenished about every 5 minutes to keep the gauze from drying.
2) Bleaching which features the use of 30% H.sub.2 O.sub.2 as the chemical agent, and the concurrent use of high frequency current on the aqueous hydrogen peroxide.
This is a method in which strips of gauze soaked in 30% H.sub.2 O.sub.2 are placed on the front surface of the teeth, and high frequency current is delivered for 1 second with the spoon-shaped tip of a high frequency scalpel. These operations are repeated 6 to 8 times every 8 seconds, during which time the H.sub.2 O.sub.2 in the gauze must be replenished to prevent it from drying.
3) Bleaching in which a paste comprising Aerosil (silica fine powder) mixed with 35% H.sub.2 O.sub.2 is used as the chemical agent, and the aqueous hydrogen peroxide and Aerosil paste is applied.
This is a method in which the aforementioned chemical agent is applied to the front surface of the teeth, which have been etched, the teeth are rinsed with water after 15 minutes, and they are then polished. In this method, the Aerosil serves as a moisturizing material to prevent the bleaching agent from drying out and further enhances the bleaching effects, resulting in high bleaching effects without the application of light or heat. The 35% H.sub.2 O.sub.2 is highly corrosive and must therefore be handled with care.
4) Bleaching in which a paste obtained by kneading a 35% H.sub.2 O.sub.2 solution and a powder (ingredients comprising potassium sulfate, manganese sulfate, silicone dioxide, or the like) is used as the chemical agent (Matsukaze Highlight, trademark).
In this method, the aforementioned chemical agent is placed on the front of the teeth and allowed to stand to bring about the action for 10 minutes thereof, or the material is irradiated with light for 3 minutes using a visible light ray radiation device. An advantage of this method is that the paste is a light green immediately after being kneaded but turns yellow when irradiated, and when the paste turns brown immediately after being kneaded, this indicates that the bleaching effects of the liquid have diminished. A drawback, however, is the same as that described above with the use of 35% H.sub.2 O.sub.2.
5) Bleaching in which a mixture of 1 mL of 30% HCl, 1 mL of 30% H.sub.2 O.sub.2, and 0.2 mL of diethyl ether is used as the chemical agent (improved MacInnes bleaching).
In this method, the aforementioned mixture is allowed to act for 5 minutes on the dental surface, and the teeth are then polished for 15 seconds under light pressure with a polishing disc. These operations are repeated 3 times, the material is then neutralized with 5.25% NaOCl, and the teeth are thoroughly rinsed with water (Oral Surg., 26: 871-878 (1968), J. Am. Dent. Assoc., 87:1329 (1973)). In this method, the paste can scatter into the eyes, making it necessary to adequately protect the patient's eyes.
6) A method in which a kneaded paste of 30% H.sub.2 O.sub.2 and a sodium perborate powder is used as the chemical agent (working bleach method).
In this method, to dilate the dentinal canaliculus and enhance the bleaching effects, the walls in the pulp cavity are treated with phosphoric acid for 1 minute, rinsed with water, and dried, and the aforementioned paste is introduced into the pulp cavity and temporarily sealed with a cement. Although this method is currently widely used for clinical purposes to which health insurance is applied as a simple, highly effective bleaching method, a drawback is the same as that described above with the use of 30% H.sub.2 O.sub.2.
Many other bleaching methods have also been reported, such as the dental bleaching agent and method comprising a mixture of aqueous hydrogen peroxide and ortho-phosphoric acid (Japanese Layed-Open Patent Application H8-143436/1996), the bleaching agent comprising a mixture of silicic anhydride with aqueous hydrogen peroxide, and the vital bleaching method comprising the application of such a bleaching agent (Japanese Layed-Open Patent Application H5-320033/1993), and the dental bleaching composition comprising a dental bleaching agent (such as hydrogen-urea peroxide, hydrogen peroxide-carbamide, and carbamide peroxide) and a matrix material (such as carboxymethylene), and a method for bleaching teeth using the above (Japanese Layed-Open Patent Application H8-113520/1996).
The following conditions are required of bleaching methods and bleaching agents during dental bleaching, however:
(a) pronounced bleaching effects; PA1 (b) the use of chemical agents that are not toxic; PA1 (c) ease of operations; PA1 (d) avoidance of detracting from dental physical properties after treatment; PA1 (e) effectiveness for both vital and non-vital methods; and PA1 (f) rapid bleaching effects. PA1 I. Food ingredients (pigments) PA1 hard water (containing iron, etc.) PA1 refreshment beverages (such as tea, coffee, cocoa, soft drinks, and red wines) PA1 II. Pigments produced by oral flora PA1 III. Tobacco PA1 IV. Metal deposition PA1 V. Chemicals (disinfectants) PA1 I. Pulp necrosis PA1 II. Bleeding in dental pulp (from external trauma, following pulpectomy, arsenious acid) PA1 III. Root canal filler components (amalgalms, silver powder, iodine, etc.) PA1 IV. Tooth decay, rheumatic fever PA1 V. Metabolic disorders PA1 (hereditary) ochronosis PA1 kaptonuria PA1 congenital dyserythropoietic anemia PA1 erythroblastosis neonatorum PA1 icterus gravis neonatorum PA1 VI. chemicals (antibiotics, root canal therapeutics) PA1 VII. hard water (containing fluorine)
A bleaching method fulfilling the above conditions would be capable of affording cosmetic improvement while preserving dental contour, with considerably improved effects.
In conventional bleaching methods, however, the primary chemical agent is 30 to 35% aqueous hydrogen peroxide, which is highly corrosive, and the oxidative action of which is the basis of bleaching.
All of the various bleaching methods currently used in Japan can be said to comprise, as noted above, a combination of 30 to 35% aqueous hydrogen peroxide, various utensils, and other chemical agents. There is an example of a bleaching method employed in the United States which features the use of 10% urea peroxide instead of 30 to 35% aqueous hydrogen peroxide, but this method is currently embroiled in controversy over problems in terms of efficacy and safety, and has yet to gain approval in Japan.
Bleaching methods covered as insured treatment are currently limited to pulpless teeth, and in some cases pulpectomy is performed on non-caries teeth for the purpose of bleaching. In addition, the use of highly toxic 30 to 35% aqueous hydrogen peroxide in various bleaching methods restricts operations and the like in a variety of ways, while limited bleaching effects for pulped teeth in particular have been indicated.
There is thus a strong need for the development of a safer, faster, simpler novel dental bleaching method that would be effective for both vital teeth and pulpless teeth.